One of the major concerns of designers of antenna system communication links is the elimination or reduction of external interference sources such as jamming, self interference, atmospheric noise, man-made noise and acoustic noise. Generally, most approaches to resolve these problems do so in a relatively complex manner.
One known approach involves the use of an antenna configuration comprised of an omnidirectional antenna and a notch antenna at the receiving end of a transmission link to cancel interference arriving from all directions except over the narrow beamwidth notch or null formed by the notch antenna. By orthogonally combining the two antenna signals, all of the undesired interference is subtracted from the signal received by the omnidirectional antenna, leaving only the desired signal. Such a system is shown and described, for example, in U.S. Pat. No. 4,275,397, entitled, "Interference Cancelling Random Access Discrete Address Multiple Access System", which issued to Frank S. Gutleber, the present inventor, on June 23, 1981. A variation of this concept is further shown and described in U.S. Pat. No. 4,431,999, entitled, "Interference Cancelling System Using A Notch And Omnidirectional Antenna", which issued to Frank S. Gutleber on Feb. 14, 1984. Both of these patents are meant to be specifically incorporated herein by reference.
Accordingly, it is an object of the present invention to provide an improvement in antenna systems having an interference cancelling capability.
It is another object of the invention to provide an improvement in antenna systems having the capability of orthogonally separating and isolating a plurality of simultaneous interference sources and substantially cancelling the signals emanating therefrom.
It is a further object of the invention to provide an antenna system which can cancel or eliminate interference from multiple sources that are offset from antenna boresight and arrive in the sidelobe region or mainlobe of a large high gain antenna.
It is still another object of the invention to provide an antenna system which provides substantial anti-jam protection for transmission links that employ large high gain antennas such as used in tropospheric line of sight links and satellite ground terminals.